iCalendar's 75-Octet Line Limit Breaks Multilingual Feeds Using Multibyte Text

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A developer building a multilingual iCalendar feed for AI model shutdown announcements discovered that the iCalendar spec (RFC 5545) enforces a 75-octet line limit, not a 75-character limit — a distinction that only surfaces when using multibyte character sets like Japanese UTF-8. While English text passed without issue, Japanese summaries silently violated the limit because each character can occupy up to 3 bytes, causing parsers to reject the feed. Fixing the issue required rewriting the line-folding logic to count bytes rather than characters, use proper CRLF line breaks, and handle multi-codepoint Unicode characters correctly. The developer also noted that calendar UIDs must be keyed on a locale-independent identifier, not localized text, to prevent duplicate events when users subscribe to multiple language feeds. A simple byte-length assertion run against a non-English test feed is recommended to catch this class of bug before deployment.

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